An isocyanate compound is useful as a raw material for the production of a polyurethane material, a polyurea material, a polyisocyanurate material and the like used in the fields of chemical, resin and paint industries.
In particular, since a plastic lens using a polyurethane material containing a sulfur atom or the like is lightweight and hardly broken as compared to an inorganic lens, and can be dyed, in late years, it has quickly come into wide use as an optical element of a spectacle lens, a camera lens and the like.
In processes for preparing important isocyanates in the various applications including a raw material of resin for the aforementioned plastic lens, further rationalization of such processes has been in demand. So, various proposals have already been made.
As the process for preparing isocyanates, a phosgene process comprising reacting a raw material amine with phosgene can be cited as a typical example. As the phosgene process, a direct process comprising directly reacting a raw material amine with phosgene, and a hydrochloride process comprising converting a raw material amine into hydrochloride and then reacting with phosgene have been widely known.
The direct process is much simpler as compared to the hydrochloride process, but urea has been generated as a by-product by reacting carbamoyl chloride or isocyanate that is an intermediate with a raw material amine in many cases. In case of the preparation of an aromatic isocyanate, since urea generated as a by-product is further reacted with phosgene to generate an isocyanate, products is obtained in relatively high yield and generation of urea is not usually a problem accordingly. However, when a linear or cyclic aliphatic amine is reacted with phosgene in the direct process, since the byproduced urea is reacted with phosgene, there has been known that a chlorine derivative is generated as a by-product (for example, refer to Patent Document 1). The chlorine derivative is usually byproduced in an amount of 3 to 10% and is sometimes byproduced as high as 20%. Hence the yield of the desired product might be decreased and the physical properties of the resin such as urethane or the like in use might be also adversely affected. So, the direct process is not usually adopted. Namely, in case of the preparation of a linear or cyclic aliphatic isocyanate, in order to suppress generation of urea as a by-product, the hydrochloride process comprising converting a raw material amine into hydrochloride and then reacting with phosgene to prepare an isocyanate has been employed (for example, refer to Patent Documents 2 to 5).
Of these Patent Documents, in Patent Document 3 to 5, there have been described processes comprising preparing an isocyanate by converting a raw material amine into hydrochloride in an organic solvent or the like in advance and then reacting with phosgene.
Patent Document 1: GB Patent No. 1086782
Patent Document 2: Japanese Patent Laid-open No. 1975-108239
Patent Document 3: Japanese Patent Laid-open No. 1999-310567
Patent Document 4: GB Patent No. 1146664
Patent Document 5: Japanese Patent Laid-open No. 2003-286241